#include <stdio.h>
#include <stdlib.h>

int main()
{
    int a[100]={0};
    int i,j,n;
    a[1]=1;
    a[2]=2;
    scanf("%d",&n);
    for(i=3;i<=n;i++)
        a[i]=a[i-1]+a[i-2];
    printf("%d",a[n]);
        return 0;
}
